Retrieve IP from DHCPD leases file instead of ARP cache (#141)

* Retrieve IP from DHCPD leases file instead of ARP cache

* Reference PLCache_read() from the retrieveRawLeases() parsing function

Sources/tart/ARP/ARPCache.swift

@@ -1,119 +0,0 @@
-import Foundation
-import Network
-import Virtualization
-
-struct ARPCommandFailedError: Error, CustomStringConvertible {
-  var terminationReason: Process.TerminationReason
-  var terminationStatus: Int32
-
-  var description: String {
-    var reason: String
-
-    switch terminationReason {
-    case .exit:
-      reason = "exit code \(terminationStatus)"
-    case .uncaughtSignal:
-      reason = "uncaught signal"
-    default:
-      reason = "unknown reason"
-    }
-
-    return "arp command failed: \(reason)"
-  }
-}
-
-struct ARPCommandYieldedInvalidOutputError: Error, CustomStringConvertible {
-  var explanation: String
-
-  var description: String {
-    "arp command yielded invalid output: \(explanation)"
-  }
-}
-
-struct ARPCacheInternalError: Error, CustomStringConvertible {
-  var explanation: String
-
-  var description: String {
-    "ARPCache internal error: \(explanation)"
-  }
-}
-
-struct ARPCache {
-  static func ResolveMACAddress(macAddress: MACAddress, bridgeOnly: Bool = true) throws -> IPv4Address? {
-    let process = Process.init()
-    process.executableURL = URL.init(fileURLWithPath: "/usr/sbin/arp")
-    process.arguments = ["-an"]
-
-    let pipe = Pipe()
-    process.standardOutput = pipe
-    process.standardError = pipe
-    process.standardInput = FileHandle.nullDevice
-
-    try process.run()
-    process.waitUntilExit()
-
-    if !(process.terminationReason == .exit && process.terminationStatus == 0) {
-      throw ARPCommandFailedError(
-        terminationReason: process.terminationReason,
-        terminationStatus: process.terminationStatus)
-    }
-
-    guard let rawLines = try pipe.fileHandleForReading.readToEnd() else {
-      throw ARPCommandYieldedInvalidOutputError(explanation: "empty output")
-    }
-    let lines = String(decoding: rawLines, as: UTF8.self)
-            .trimmingCharacters(in: .whitespacesAndNewlines)
-            .components(separatedBy: "\n")
-
-    // Based on https://opensource.apple.com/source/network_cmds/network_cmds-606.40.2/arp.tproj/arp.c.auto.html
-    let regex = try NSRegularExpression(pattern: #"^.* \((?<ip>.*)\) at (?<mac>.*) on (?<interface>.*) .*$"#)
-
-    for line in lines {
-      let nsLineRange = NSRange(line.startIndex..<line.endIndex, in: line)
-
-      guard let match = regex.firstMatch(in: line, range: nsLineRange) else {
-        throw ARPCommandYieldedInvalidOutputError(explanation: "unparseable entry \"\(line)\"")
-      }
-
-      let rawIP = try match.getCaptureGroup(name: "ip", for: line)
-      guard let ip = IPv4Address(rawIP) else {
-        throw ARPCommandYieldedInvalidOutputError(explanation: "failed to parse IPv4 address \(rawIP)")
-      }
-
-      let rawMAC = try match.getCaptureGroup(name: "mac", for: line)
-      if rawMAC == "(incomplete)" {
-        continue
-      }
-      guard let mac = MACAddress(fromString: rawMAC) else {
-        throw ARPCommandYieldedInvalidOutputError(explanation: "failed to parse MAC address \(rawMAC)")
-      }
-
-      let interface = try match.getCaptureGroup(name: "interface", for: line)
-      if bridgeOnly && !interface.starts(with: "bridge") {
-        continue
-      }
-
-      if macAddress == mac {
-        return ip
-      }
-    }
-
-    return nil
-  }
-}
-
-extension NSTextCheckingResult {
-  func getCaptureGroup(name: String, for string: String) throws -> String {
-    let nsRange = self.range(withName: name)
-
-    if nsRange.location == NSNotFound {
-      throw ARPCacheInternalError(explanation: "attempted to retrieve non-existent named capture group \(name)")
-    }
-
-    guard let range = Range.init(nsRange, in: string) else {
-      throw ARPCacheInternalError(explanation: "failed to convert NSRange to Range")
-    }
-
-    return String(string[range])
-  }
-}

Sources/tart/Commands/IP.swift

@@ -38,7 +38,7 @@ struct IP: AsyncParsableCommand {
     let vmMacAddress = MACAddress(fromString: config.macAddress.string)!
 
     repeat {
-      if let ip = try ARPCache.ResolveMACAddress(macAddress: vmMacAddress) {
+      if let ip = try Leases().resolveMACAddress(macAddress: vmMacAddress) {
         return ip
       }
 

Sources/tart/MACAddressResolver/Lease.swift

@@ -0,0 +1,32 @@
+import Network
+
+struct Lease {
+  var mac: MACAddress
+  var ip: IPv4Address
+
+  init?(fromRawLease: [String : String]) {
+    // Retrieve the required fields
+    guard let hwAddress = fromRawLease["hw_address"] else { return nil }
+    guard let ipAddress = fromRawLease["ip_address"] else { return nil }
+
+    // Parse MAC address
+    let hwAddressSplits = hwAddress.split(separator: ",")
+    if hwAddressSplits.count != 2 {
+      return nil
+    }
+    if let hwAddressProto = Int(hwAddressSplits[0]), hwAddressProto != ARPHRD_ETHER {
+      return nil
+    }
+    guard let mac = MACAddress(fromString: String(hwAddressSplits[1])) else {
+      return nil
+    }
+
+    // Parse IP address
+    guard let ip = IPv4Address(ipAddress) else {
+      return nil
+    }
+
+    self.ip = ip
+    self.mac = mac
+  }
+}

Sources/tart/MACAddressResolver/Leases.swift

@@ -0,0 +1,106 @@
+import Foundation
+import Network
+
+enum LeasesError: Error {
+  case UnexpectedFormat(name: String = "unexpected DHCPD leases file format", message: String, line: Int)
+  case Truncated(name: String = "truncated DHCPD leases file")
+
+  var description: String {
+    switch self {
+
+    case .UnexpectedFormat(name: let name, message: let message, line: let line):
+      return "\(name) on line \(line): \(message)"
+    case .Truncated(name: let name):
+      return "\(name)"
+    }
+  }
+}
+
+class Leases {
+  private let leases: [MACAddress : Lease]
+
+  convenience init() throws {
+    try self.init(URL(fileURLWithPath: "/var/db/dhcpd_leases"))
+  }
+
+  convenience init(_ fromURL: URL) throws {
+    let fileContents = try String(contentsOf: fromURL, encoding: .utf8)
+
+    try self.init(fileContents)
+  }
+
+  init(_ fromString: String) throws {
+    var leases: [MACAddress : Lease] = Dictionary()
+
+    for lease in try Self.retrieveRawLeases(fromString).compactMap({ Lease(fromRawLease: $0) }) {
+      leases[lease.mac] = lease
+    }
+
+    self.leases = leases
+  }
+
+  /// Parse leases from the host cache similarly to the PLCache_read() function found in Apple's Open Source releases.
+  ///
+  /// [1]: https://github.com/apple-opensource/bootp/blob/master/bootplib/NICache.c#L285-L391
+  private static func retrieveRawLeases(_ dhcpdLeasesContents: String) throws -> [[String : String]] {
+    var rawLeases: [[String : String]] = Array()
+
+    enum State {
+      case Nowhere
+      case Start
+      case Body
+      case End
+    }
+    var state = State.Nowhere
+
+    var currentRawLease: [String : String] = Dictionary()
+
+    for (lineNumber, line) in dhcpdLeasesContents.split(separator: "\n").enumerated().map({ ($0 + 1, $1) }) {
+      if line == "{" {
+        // Handle lease block start
+        if state != .Nowhere && state != .End {
+          throw LeasesError.UnexpectedFormat(message: "unexpected lease block start ({)", line: lineNumber)
+        }
+
+        state = .Start
+      } else if line == "}" {
+        // Handle lease block end
+        if state != .Body {
+          throw LeasesError.UnexpectedFormat(message: "unexpected lease block end (})", line: lineNumber)
+        }
+
+        rawLeases.append(currentRawLease)
+        currentRawLease = Dictionary()
+
+        state = .End
+      } else {
+        // Handle lease block contents
+        let lineWithoutTabs = String(line.drop { $0 == " " || $0 == "\t"})
+
+        if lineWithoutTabs.isEmpty {
+          continue
+        }
+
+        let splits = lineWithoutTabs.split(separator: "=", maxSplits: 1)
+        if splits.count != 2 {
+          throw LeasesError.UnexpectedFormat(message: "key-value pair with only a key", line: lineNumber)
+        }
+        let (key, value) = (String(splits[0]), String(splits[1]))
+
+        currentRawLease[key] = value
+
+        state = .Body
+      }
+    }
+
+    if state == .Start || state == .Body {
+      throw LeasesError.Truncated()
+    }
+
+    return rawLeases
+  }
+
+  func resolveMACAddress(macAddress: MACAddress) throws -> IPv4Address? {
+    leases[macAddress]?.ip
+  }
+}

Sources/tart/MACAddressResolver/MACAddress.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-struct MACAddress: Equatable, CustomStringConvertible {
+struct MACAddress: Equatable, Hashable, CustomStringConvertible {
   var mac: [UInt8] = Array(repeating: 0, count: 6)
 
   init?(fromString: String) {

Tests/TartTests/MACAddressResolverTests.swift

@@ -0,0 +1,35 @@
+import XCTest
+import Network
+@testable import tart
+
+final class MACAddressResolverTests: XCTestCase {
+  func testSingleEntry() throws {
+    let leases = try Leases("""
+                            {
+                              ip_address=1.2.3.4
+                              hw_address=1,00:11:22:33:44:55
+                            }
+                            """)
+
+    XCTAssertEqual(IPv4Address("1.2.3.4"),
+      try leases.resolveMACAddress(macAddress: MACAddress(fromString: "00:11:22:33:44:55")!))
+  }
+
+  func testMultipleEntries() throws {
+    let leases = try Leases("""
+                            {
+                              ip_address=1.2.3.4
+                              hw_address=1,00:11:22:33:44:55
+                            }
+                            {
+                              ip_address=5.6.7.8
+                              hw_address=1,AA:BB:CC:DD:EE:FF
+                            }
+                            """)
+
+    XCTAssertEqual(IPv4Address("1.2.3.4"),
+      try leases.resolveMACAddress(macAddress: MACAddress(fromString: "00:11:22:33:44:55")!))
+    XCTAssertEqual(IPv4Address("5.6.7.8"),
+      try leases.resolveMACAddress(macAddress: MACAddress(fromString: "AA:BB:CC:DD:EE:FF")!))
+  }
+}